Coin recognition apparatuses that transport coins by a transporting mechanism and perform recognition of a denomination and/or authenticity of each coin by a magnetic sensor including an oscillator coil and a receiving coil that are arranged across a transport path from each other are known in the art.
For example, a technology for recognizing a coin is disclosed in Patent Document 1. In this technology, a synthesized signal containing signals of a plurality of frequencies is applied to an oscillator coil as an input signal, a signal that is induced in a receiving coil is output from a receiving side as an output signal, and coin recognition is performed based on comparison of the input signal and the output signal.
Specifically, an oscillation signal of a high frequency (for example, 250 kilohertz (kHz)), an oscillation signal of a medium frequency (for example, 16 kHz), and an oscillation signal of a low frequency (for example, 4 kHz) are synthesized and applied to the oscillator coil.
On the receiving side, the high frequency signal (for example, 250 kHz) in the signal that is induced in the receiving coil is separated by using a first filter, the medium frequency signal (for example, 16 kHz) is separated by using a second filter, and the low frequency signal (for example, 4 kHz) is separated by using a third filter.
Then, the signals of each frequency (250 kHz, 16 kHz, and 4 kHz) contained in the synthesized wave are extracted. The signals of each of the frequencies (250 kHz, 16 kHz, and 4 kHz) on the receiving side and the transmitting side are compared each other, and recognition of the denomination and/or authenticity of the coin are performed based on attenuation characteristics of the signals.    [Patent document 1] Japanese Patent No. 3995423